Electroacoustical transducers are advantageous because they provide a conversion between electrical energy and acoustical energy. For example, when alternating current signals are introduced to an electroacoustical transducer, the transducer vibrates and produces acoustical energy in accordance with such vibrations. The conversion of electrical energy to acoustical energy has a number of different uses such as in loud speakers and in sonar applications, for example.
Piezoelectric elements, primarily crystals and ceramics, are employed in a variety of devices including crystal microphones, ultrasonic devices, accelerometers and oscillators. One of the most common uses of piezoelectric elements is in underwater sonar equipment in which a piezoelectric sonar transducer is stimulated by electrical signals to emit sonar signals which radiate out from the transducer. The sonar signals are reflected off of underwater objects and the reflected signals are then detected by the transducer, which in turn produces and delivers electrical signals carrying information about the underwater object.
Flextensional sonar transducers of the prior art may employ a stack of piezoelectric transducer elements interspersed with electrically conducting plates for stressing the elements and for picking up electrical current produced by the elements; a prestressed compression band, made for example of a filament wound material, wrapped about the piezoelectric stack; and an outer elliptically-shaped shell wrapped about the compression band. The stack of piezoelectric elements generally extends along the major axis of the ellipse defined by the outer shell. When an alternating voltage is applied to the conducting plates, the stack of piezoelectric elements is caused to be displaced in the direction of the major axis in proportion to the instantaneous value of the voltage. The vibration and displacement of the stack is transmitted to the shell which amplifies the vibration along the minor axis of the ellipse to produce the sonar signals. That is, as the stack expands to expand the major axis of the ellipse, the long walls of the ellipse perpendicular to its minor axis contract, and as the stack contracts to expand the long walls of the ellipse, vibration of the shell necessary to generate the sonar is produced. In an alternative arrangement of a flextensional transducer, a magnetostrictive element may replace the piezoelectric stack.
The elliptical shells used in flextensional transducers are typically preformed of filament-wound composites such as glass, reinforced plastic or aluminum. In order to incorporate the stack of piezoelectric elements in the shell, the shell is compressed along its minor axis by means of a press, and the piezoelectric stack is inserted into the shell to coincide with the major axis. Upon removal of the compressive force from along the minor axis, a residual force remains in the shell to retain the stack and apply a predetermined compressive stress thereto. Construction of the assembly in this fashion requires the piezoelectric stack and elliptical shell be prepared to close tolerances both to allow for easy insertion of the stack within the compressed shell, and to retain tight contact between the stack and the shell upon removal of the compressive forces.
Slotted Cylinder Projectors or SCPs, have been used to provide low frequency transducer devices capable of operating in the low frequency range (about 425 Hz and below). More particularly, compact SCPs having diameters less than or equal to T-size (i.e. 12.75 inch outer diameter) have been used for such low frequency range operation. However, these SCPs exhibit a very narrow bandwidth which limits the breadth of operation of such devices. In addition, high power SCPs require a great number of segmented 33-mode rings, each of which is formed from multiple wedges. This causes difficulty in both the initial manufacturing process (which is very labor intensive), as well as in the prestress portion and installation into the inert shell. Furthermore, such SCPs exhibit reliability problems resulting from the unsupported gap or slot therein. FIG. 1 is an illustration of a prior art transducer device 10 having an inert tubular member 12 with a gap 14 and a plurality of sectionalized transducer elements 16 arrayed within the member 12 in abutting and progressive relationship to one another and in abutting relationship to the inner wall of the member 12. The gap is typically covered with a thin boot to avoid suppressing motion. The unsupported gap causes high stress risers in the ceramic which results in ceramic failure and flooding failure into the gap region. Moreover, the high velocity near the gap region often results in undesirable cavitation. A cylindrical transducer which overcomes one or more of the aforementioned difficulties is highly desirable.